Constant speed mechanism



March 13, 1934. H. E. NICHOLS 1,950,310

CONSTANT SPEED macmmsm Original Filed May 4, 1927 Patented Mar. 13, 1934 PATENT OFFICE CONSTANT SPEED MECHANISM Horace E. Nichols, Detroi t,Mich., assignor of onethird to Clyde Harrison Chase and one-third toHugo A. Freund, both of Detroit, Mich.

Original application May 4, 1927, Serial No. 188,839. Divided and thisapplication April 17, 1933, Serial No. 666,499

19 Claims. (Cl. 112 284) The present invention relates to improvementsin constant speed mechanisms, such, for instance, as may beadvantageously used in connection with electrocardiographs, heliographs,helio-- 5 tropes, and other types of light flashing apparatus. Forinstance, in an electrocardiograph a light beam is projected on a mirrorand reflected through a driven slitted shutter or flasher on to asensitized film, and a motor or other source of power is employed forrevolving the apertured shutter or flasher. Such an instrument isemployed for making a visible and permanent record of heart actions andconsequently the speed at which the apertured shutter or flasher isrevolved must be constant in order to determine time intervalsthroughout a diagnosis of the action of the heart. Other instances oftiming may be in connection with the interruption or reflection of lightbeams, the operation of clock dials 2 and time switches, and thecontrolling of relays and of maximum demand meters.

The driving of such shutter, for instance, from a power source and insynchronism with the latter, would be a simple matter of proper gearrelationships, if the speed of the power source were assuredly constantin rate, so as to present no variation in the rate of speed. Thedifficulty arises because of the condition that power source operationhas not reached a stage of development where the exact constancy in rateof speed is present, although the variations in rate may be small. Undermost conditions of operation these minor variations become unimportant,but in structures of the type above referred to it is essential that therecords obtained be accurataand to produce this result it becomesnecessary that the rate of speed of the driven element-the shutter, forinstance-be constant with exactness, it possible, regardless of powervariations in 40 speed, and it is to meet this condition that thepresent type of invention, has been developed, it being designed tointerpose, within the line from the driving structure to the drivenmember or element, a mechanism which will automatically detect and tocompenate for the rate changes. It should be noted that the ratevariations referred to are not those which come from adjustment of thepower source itself--these latter are not being considered so far as thepresent invention is concerned; the variations referred to are thoseinherently present when the power source is, operating at an assumedconstant speed, and are variations which are small as a general rule,but which, in the production of an accurate record,

for instance, would materially affect the accuracy of the record.

The present application is a division of an application filed May 4,1927, Serial No. 188,839, patented April 18, 1933, No. 1,903,832 inwhich the structure herein disclosed is one of the modiflcationsdisclosed therein, the general principles underlying the solution oftheparticular problems involved, being capable of being employed instructures of different'types, one of which is that disclosed in thepresent invention. The parent application discloses more particularlythe detailed characteristics of the problem to be solved and the generalmethods employed in its solution,

and this detailed explanation is not repeated herein. For the purpose ofa general explanation, however, a brief synopsis of the fundamentals ofthe solution are presented herein, to permit a clearer understanding ofthe present invention and its particular manner of solving the Tlgeneral problems involved.

The underlying features of the general solution may be briefly stated asfollows:

If the operating connections between the drive source and the drivenelement be of fixed character, it is evident that any variations inspeed rate of the drive source are necessarily made manifest on thedriven member; if the proportional speed between the two elements beamplified, any inaccuracies in the rate of the drive source will beamplified in the driven element, and vice versa. To correct thiscondition, this general solution of the problem contemplates thelocation within this line of operating connections of a mechanism whichwill instantly detect the presence of such variations .in the rate 01speed of the drive source and set in motion a change in conditionswithin the connections such as will so vary the operation of theconnections that the rate of speed of the driven element will not bechanged. In other words, no attempt is made to change the operation ofthe power source-the correction is made within the connections betweensuch source and the driven element.

Fundamentally, this result is produced by placing within the line 0!connections a mechanism which presents the drive and driven parts as inmore or less opposition and to then set up the development of adifferential action characteristic between them. This may take the formof using an actual difierential mechanism structure within theconnections and employing a controlling mechanism for the differentialonthe power side of the differential, the control mechanism beingoperative on the differential; such structure no forms thesubject-matter of a companion application filed concurrently herewith,Serial No. 666,497. Or it may be in the form of a structure in which thecontrol mechanism its if performs the function of the differentialaction, this particular development being found in a number of forms,one of which is disclosed and claimed in the parent application, asecond form being disclosed in my companion application filedconcurrently herewith, Serial No. 666,498, and a third forming thesubject-matter of the present application.

The structures of the companion applications each involve the use of afixed load characteristic on one side and a variable load characteristicon the opposite side of an intermediate portion of the connections,these twoload conditions being effective in theoperation of the controlmechanism and in which the variations in speed are operative to controlthe variations of the variable load. These loads are in the form ofmagnetic fields in which are mounted elements in such manner that arelative movement of the elements within the field can be had. In thefixed load condition, the element is rotative at a constant speed sothat the load remains constant; in the variable load the element ismovable in such manner that the number of lines of force of the fieldcutting the movable element are varied and thus affect the retardationvalue of the field on the element and consequently the load value of thefield and element. The third element is a control mechanism between thetwo loads, and which is active in varying the variable load by thevariations in speed of the drive source; this control mechanism is ofvarious types, and detects the presence of the rate changes, and byvarying the variable load produces the compensation that is necessary topreserve the constancy in the rate of speed of the driven element.

In the present invention, the same general results are obtained, but thearrangement differs somewhat in that both the constant and the variableloads are on the same side of the control mechanism, the latter beinglocated between the power and the variable load.

The present invention therefore consists in the improvedconstruction andcombination of parts, hereinafter described, illustrated in theaccompanying drawing, and more particularly pointed out in the appendedclaims.

In the accompanying drawing, in which similar reference charactersindicate corresponding parts in each of the views:

Figure 1 is a vertical sectional view, partly in elevation, of theparticular embodiment of the invention disclosed herein, and

Fig. 2 is a sectional view thereof on line 22 of Fig. 1.

In the drawing, 10 indicates what may be termed the drive shaft, thisextending vertically from a base 11, a bracket 12 forming a bearingsupport for the shaft. The shaft is driven from a suitable source and insuitable manner, a pulley 13 being shown as the means by which the shaftis rotated. The shaft carries one of the elements of what I term anelectromagnetic governor, this element being in the form of a screw 14having coarse threads 14a. Co-operating with this screw is a nut 15, theinterior of which is adapted to co-operate with the threads 14a, as bythe presence of balls 15a which enter the threads 14a. Y

The nut 15 carries a plate 16 having a downwardly-projecting flange16a,the nut and plate forming what I term a drag member which, in connectionwith the screw, sets up a sensitive governing action when employed withthe structure presently described. With the parts at rest, for instance,rotation of shaft 10 will initially cause the threads 14a to raise thenut, since the latter is at a state of rest. As the nut raises, however,its weight becomes effective to produce the effect of running down hill"with the result that the nut will be rotated although there is no directdrive connection therebetween. While the nut can attain a speed tooverrun the shaft, due to the weight factor of the nut, it can beunderstood that if the speed of the nut can be limited relative to theshaft speed, the nut can take up a position of equilibrium relative tothe screw with the nut and screw traveling at a synchronous speedrelation. And, if the drag characteristic which forms the speed-limitingfactor of the nut, is variable, the position of equilibrium of the nutis also variable.

The latter condition is produced by providing a succession of polepieces 1'1, these being shown as in the form of permanent magnets havingop-' posed poles with a gap between the poles, these pole pieces beingof suitable number and arranged in a circular series, as indicated inFig. 2. The plate 16 with its flange 16a is of non-magnetic material,and, in operation, the flange is operative relative to the gap betweenthe poles. As will be obvious, the greater the number of magnetic linesof the magnetic field of the gaps which may be cut by the flange 16a,the greater will be the drag efiect present on the nut.

In the present form of the invention, the magnets are carried by aninverted cup-shaped member 18 mounted on what may be termed the drivenshaft 19, the latter being supported in suitable manner, as by bearings,one of which may be a bearing at the upper end of the drive shaft 10, 5the two shafts being free to rotate relatively. Shaft 19 also carries aplate 20 which extends into the gap between the poles of a permanentmagnet 21, the latter constituting the fixed load of the, structure,since the load value is constant.

As will be understood, the pole pieces 1'1 and flange 16a provide thecharacteristics of the variable load, since the position of the flange16a is variable within the magnetic field. For instance, with the partsat rest, and shaft 10 beginning its rotation, the immediate effect is toraise the nut 15; the latter may move the fiange'out of the magneticfield, thus permitting the gravitation effect of the weight of the nutto cause the latter to try to run down by overunning the speed of thescrew. As soon as the flange enters the magnetic field, the drag effectof the latter affects the speed of the nut, with the result that thereis a tendency to produce the conditions of a point of equilibriumbetween nut and screw, this point being automatically determined by atendency to balance the forces involved.

However, an additional factor is presented by the fact that thepolepieces are also capable of being moved in the circular path, beingcarried 1 by the rotatable shaft 19, so that the drag effect set up bythe movement of flange 15a within the gaps tends to set up movement ofthe pole pieces in the circularpath, the slippage condition presentbeing determined by the amount of magnetic' 5 or torque reaction beingproduced by the co-operating poles and flange. Since the slippagebecomes less pronounced as the speed of the driven shaft increases, theeffect is carried into the relations of nut and screw, until the drivenshaft 19 50 reaches its desired speed which is determined by the fixedload. During this development, the nut will gradually work to a positionof equilibrium determined by all of the factors, at which time thedriven shaft will be rotated at the desired speed by the drive shaft andwill continue to do so as long as the speed of the drive shaft remainsconstant.

However, the speeds of power sources may vary, even though slightly, andit is to meet this condition that the present type of invention isutilized, since it is essential that the driven shaft be rotated atunvarying speed. ,This result is obtained in the present invention. Forinstance, should the speed of the drive shaft increase, this fact willbe instantly manifest through the increase in speed of the screw, withthe consequent effect of tending to raise the nut and decreasing themagnetic or torque reaction present, thus disturbing the point ofequilibrium which the nut will seek to restore. Should the speed of thedrive shaft decrease, the gravitation effect becomes immediatelyeffective to increase the magnetic or torque reaction effect and thushold the driven shaft to its speed. In each case, steady running of thedrive shaft after the change sets upthe conditions of equilibrium tocontinue the unvarying rotation of the driven shaft. Since the combinedaction of the threads and the weight of the nut are constantly active todetect speed changes of the drive shaft, and the position of the nut isresponsive to the conditions produced by the change, with the positionof the nut active in determining the magnetic or torque reaction, it canbe readily understood that the governor effect set up is exceedinglysensitive to speed changes even though the latter be slight, with theresponse made with such rapidity that the speed of the driven shaftremains unaffected by the speed change of the drive shaft.

In other words, the structure is designed more particularly to meet theconditions of small variations in drive speed and produce instantaneousresponse. For the particular service for which the invention isdesigned, in which the slightest change in driven shaft speed couldserve to affect the records being made, it can be understood that ahighly sensitive govemer be present as a part of. the connectionsbetween the drive and driven shafts. The apparatus is generally employedunder assumedly constant power speed conditions, so that any variationsare generally small, but even these must be compensated for to obtainthedesired records.

As will be understood, the torque reactions produced by the rotation ofplates 16 and 20 in the respective magnetic fields differ in that thetorque.

reaction in connection with plate 20 is constant while that of plate 16is variable, thus producing the effect of fixed and variable loads.

Because of the particular mounting of nut 15 and the relation of itsflange 16a with the magnetic field produced by the pole pieces 17, thenut and plate may be considered as a floatable member with the floatingmovements in a fixed path. Because of this characteristic there is nodirect and positive drive connection between the two shafts, the drivebeing through the torque reaction effect produced by the rotation of theflange 16a within the gap between the pole ends. Hence, the drlveactionis through a fioatable element having no fixed position relative toeither the drive or driven elements, but is an element which is variablein position and constantly seeking a 1 position of equilibrium throughthe activity of the various forces involved, the "hunting" eii'eet beingmade manifest at all times during rotationvofthedriveshaft;iifthespeedofthelatteris and whenever this is presentit tends to prevent the nut from exceeding the relative speed omentialin producing this effect. This drag eflect causes the thread to tend toraise the nut, in the event of an increased speed of the drive shaft,

and thus reduce the drag effect and permit greater slippage; if thedrive shaft speed decreases, the tendency is for the nut to run down"the thread, thus increasing the drag eil'ect and reducing the slippage.

It will be understood, of course, that in service. the structure ispermitted to develop the driven shaft speed to its proper point beforethe apparatus with which it is being used is rendered active for themaking of the record. The drive shaft remains active until the recordhas been completed and the apparatus rendered inactive. Hence, thetiming action, for which the structure is particularly adapted, takesplace only during the period when the driven shaft isdriven at thepredetermined speed; when the structure is employed with a cardiograph,for instance, the period of recording may be a matter of minutes, duringwhich period it is essential that the driven shaft speed be maintainedconstant.

The complete mechanism of the' apparatus is not disclosed herein,although indicated in greater detail in the parent application, thepresent invention being more particularly to the sensitive driveconnection between the shafts. However, for illustrative purposes, Ihave shown a bracket 24 carrying mirrors 25 adapted to project lightrays through apertures in the plate 20 the latter having thecharacteristics of a shutter in the operation of the apparatus.

While I have herein shown and described a preferred form of theinvention and a modification of the broad invention disclosed in theparent application, it is obvious that changes and modi- I ficationstherein may be found desirable or essential in meeting the exigencies ofuse, and I desire to be understood as reserving the right to make anyand all such changes or modifications as may be found desirable ornecessary, insofar as the same may fall within the spirit and scope ofthe invention as expressed in the accompanying claims when broadlyconstrued.

Having thus described my invention, what I claim as new is:

1. In timing mechanism wherein the speed of a driven shaft is maintainedconstant regardless of speed changes of the driving shaft, a drivenshaft having a load of constant value to produce a torque reactionconstant in value, a drive shaft, and means responsive to drive speedsof the drive shaft for automatically producing an independ-. ent torquereaction within the means with the value of the latter torque reactiondetermined by the speed of the drive shaft and variable in presence ofdrive speed variations and with such torque reaction compensatory to thespeed variations, said means including a load active in producing thetorque reaction and variable as to value by variations in drive speed,such loadincluding a member and a magnetic field movable relatively toeach other, and means for supporting said member on the drive shaft insuch manner as to permit relative movement therebetween rotatively andaxially during load production activity.

-2. Mechanism as in claim 1 characterized in that the axis of membermovement is vertical with the weight of the member providing a gravitycomponent co-operative with the drive shaft speed in producing therelative movements of drive shaft and member.

3. Mechanism as in claim 1 characterized in that the supporting meansfor the member includes a pair of opposing faces movable relatively toeach other helically about the drive shaft axis.

4. Means as in claim 1 characterized in that the supporting means forthe member includes a pair of faces movable relatively to each otherhelically about the drive shaft axis, the axis of such faces extendingvertically, the weight of the member and the drive shaft speedco-operating in the relative movements of the faces in the direction ofthe helix.

5. Mechanism as in claim 1 characterized in that the magnetic field iscarried by and movable with the driven shaft.

6. Mechanism as in claim 1 characterized in that the magnetic field iscarried by and movable with the driven shaft, movement of the magneticfield being provided by movements of the member through the torquereaction relation between member and field.

7. In timing mechanism and in combination, a driven shaft having a fixedload characteristic, a drive shaft, and means operatively' connectingsaid shafts to produce driven shaft rotation at constant speedregardless of limited variations in speed of the drive shaft, said meansincluding a magnetic field carried by and movable with the driven shaft,and a member carried by and floatable rotatively relative to the driveshaft, said member and magnet field being co-operative to provide avariable load characteristic by the relative rotation of drive shaft andmember, the floating movements of the member being in a definite path.

8. A combination as in claim 7 characterized in that relative rotationof drive shaft and member is operative to shift the member axially ofthe drive shaft.

9. A combination as in claim 7 characterized in that relative rotationof drive shaft and member is operative to shift the member axially ofthe drive shaft and vary the relation of the member to the magneticfield.

10. A combination as in claim 7 characterised, in that the memberincludes a flange movable in the magnetic field rotatively and axially.

11. A combination as in claim 7 characterize in that the member includesa flange movable in the magnetic field rotatively and axially, the valueof the flange activity with the field in producing the variable loadcharacteristic being determined b; the relative rotation of member anddrive s aft.

12. A combination as in claim 7 characterized in that the member anddrive shaft are operatively connected helically with the helix formationhaving a vertical axis, whereby gravitation of the member is active inproviding relative rotational movement of drive shaft and member.

13. In combination, a rotatable driven element having a magnetic field,a drive shaft, and a member carried by and movable rotatively andaxially relative to said shaft and being cooperative with said field indriving the driven element.

14. A combination as in claim 13 characterized in that the value of thedrive activity between member and field is determined by the axialposition of the member relative to the drive shaft.

15. A combination as in claim 13 characterized in that the value of thedrive activity between member and field is determined by the axialposition of the member relative to the drive shaft with such axialposition determined by the relative rotation of drive shaft and member.

16. -A combination as in claim 13 characterized in that the drive shaftand member are operatively connected to permit'gravitational activity ofthe member in providing relative rotational movements therebetween.

17. 'A combination as in claim 13 characterized in that the member anddrive shaft are operatively connected to permit relative rotation in ahelical path.

18. A combination as in claim 13 characterized in that the member anddrive shaft are operatively connected to permit relative rotation in ahelical path with such path located to cause the weight of the member toprovide relative rotation in one direction by gravitation.

19. A combination as in claim 13 characterized in that the member anddrive shaft are operatively connected to permit relative rotation in ahelical path with such patn located to cause the weight of the member toprovide relative rotation in one direction by gravitation, relativerotation in the opposite direction being provided by drive shaftrotation.

HORACE E. NICHOLS.

